Thin-film magnetic recording media have been increasingly and extensively used in the manufacturing of hard disks to facilitate read/write operations in computers. Thin-film magnetic recording media are typically prepared by sputtering a thin magnetic film, or the so-called magnetic recording layer, on a substrate, which is typically a textured aluminum or Ni/P substrate. A chromium or chromium-alloy underlayer is typically provided which is sandwiched between the magnetic recording layer and the substrate. After the magnetic recording layer is sputtered on the chromium underlayer, a protective overcoat layer, which is typically an amorphous carbon film (a:C), is then applied over the metal alloy magnetic recording layer, also by sputtering. The magnetic recording layer can be cobalt-based alloy.
As the need as well as consumers' appetite for higher density recording media become more and more demanding, the flying height of the magnetic head is forced to become lower and lower, to the level of "near to contact", relative to the magnetic recording media. As a result, the mechanical strength and the tribological characteristics of the protective layer have become an important topic in order to further improve the performance, including the recording density, of the magnetic recording media.
It was discovered by J. K. Lee et al that the presence of a sufficient amount of hydrogen in the sputtering chamber could result in a carbon film which will exhibit superior mechanical characteristic. See J. K. Lee et al, IEEE Transactions on Magnetics, Vol 29, No. 1, January 1993. It was also predicted that carbon nitride film could be harder than a diamond film. See, e.g., A. Y. Liu and M. L. Cohen, Science 245, 841 (1989). Their prediction was supported by the observations of Andrei Khurshuov and Tse-An Yeh et al, who reported that carbon nitride material has the characteristics of high hardness, high wear resistance, and low friction. See Andrei Khurshudov et al, J. Vac. Sci. Technol. A14 (5), September/October 1996, and Tse-An Yeh et al. IEEE Transaction on Magnetics, Vol 27, No. 6, November 1991.
While hydrogen and nitrogen showed beneficial results when they are individually introduced into the sputtering chamber during the preparation of the amorphous carbon overcoat, there have not been any prior art reports which would suggest a commingling of these two gases. The reason may be due to some adverse effects that might have been observed when the hydrogen gas is mixed with the nitrogen gas in the sputtering chamber. One notable deterrence against commingling the hydrogen gas with the nitrogen gas is that the presence of hydrogen in a nitrogen doped film would cause the contact angle to be increased, thus adversely affecting the tribological characteristic of the amorphous carbon film.
With the capacity of the hard disks now being in the gigabytes range, every element of the hard disk is important. The mechanical and tribological properties of the overcoat film can greatly affect the gliding height of the magnetic head as well as the service life of the magnetic recording disk. Thus, it is important to explore new way to further improve the characteristics of the amorphous carbon overcoat film.